2009 pulleys

Notes: Pulleys, wheel and axles and gears

H: Review Notes

Pulleys, Wheel and axle and Gears

April 20, 2009

Objectives

1. Define pulley, wheel and axle, and gear

2. Compare fixed, movable and compound pulleys

3. Calculate the MA of pulleys and a wheel and axle

Pulleys• A pulley is a rope,

belt or chain wrapped around a grooved wheel.

• Pulleys are modified forms of a first class lever.

MA of a Pulley

MA = number of lines supporting the load

MA = 1

One line is supporting the load.

MA = 2

Two lines are supporting the load.

Types of Pulleys

Fixedcompound

moveable

Fixed Pulleys

A fixed pulley is a pulley that is attached to something that does not move.

Fixed pulleys change the direction of the force in a rope (called a belt when it goes in a full circle) but not the size of the force.

mechanical advantage of 1

Moveable Pulley

The load is supported by 2 rope arms under the pulley. You must pull 2 times the distance to lift the load.

The effort arm will always be twice the length of the resistance arm so the mechanical advantage of a single moveable pulley is 2.

Compound Pulley

Two (or more) pulleys can be arranged to work together

Allows the user to gain both Mechanical and Directional Advantage. The more rope arms supporting the load the greater the Mechanical Advantage.

Block and tackle

A compound pulley where several pulleys are mounted on each axle, further increasing the mechanical advantage.

The Wheel and Axle

• Two or more wheels are connected by an axle.

• The wheel turns with or around the axle.

Wheel & Axle M.A.

M.A. = Wheel Circumference

Axle Circumference

Example: 10 in = 5 2 in

2"

10"

Gears

A gear is a wheel with teeth that fit in between each other and turn.